FSetProperty::InstanceSubobjects and FMapProperty::InstanceSubobjects mutate containers but don't reshash them

Yeah, there’s no way to catch or handle all possible misuses of ‘weak’ or ‘dynamic’ key types to our associative containers other than basically removing `GetTypeHash` and `operator==` for such types to stop them being usable as keys in the first place, and that would break a lot of legacy usage. We do keep these issues in mind as we evolve our Core systems to allow better constructs.

Steve